The invention relates to monolithic catalyst support structures formed of alumina, and particularly to theta-alumina coated monolith supports for catalytic reactions involving hydrogenation including pyrolysis gasoline hydrogenation and hydrotreating.
In a hydrocarbon process such as pyrolysis gasoline hydrogenation for the removal of olefinic impurities from gasoline, theta alumina phase is desirable due to its low surface acidity and reduced tendency to form coke with olefinic impurities. It is particularly effective for selective hydrogenation such as di-olefine hydrogenation, Cat-Naphtha hydrogenation to preserve its octane number, acetylene hydrogenation into ethylene, removal of olefines from aromatics, etc. as some examples but not limited to these listed examples.
Despite the numerous benefits of theta alumina, there are limited commercial resources available for these products. This is especially true for monolithic catalyst supports comprising high percentage of alumina in theta crystalline phase. Catalyst supports having a coating of theta alumina generated in-situ are more effective when compared to catalyst supports having a washcoated theta alumina layer. By “in situ theta alumina” is meant theta alumina formed or synthesized from alumina precursors on site.
Consequently, the coating of ceramic monoliths with a film or washcoat of alumina is relatively easy and has been practiced in automotive catalyst industry for many years. There are many patents covering the detailed coating compositions and their processing. The following offers a brief summary of the prior art.
U.S. Pat. Nos. 3,554,929, 4,039,482, 4,208,454, and 4,550,034 disclose techniques of washcoating substrates or supports including alumina material washcoating. However, the referenced patents do not teach in situ synthesized theta alumina formed as the main phase in the coating of the monolithic support body, i.e., over 50% by weight of the composition.
U.S. Pat. No. 4,529,718 discloses a washcoated monolith structure with alumina or its precursor materials in aqueous slurry or solution to form a catalyst support. Based on this disclosure, the washcoated alumina layer formed on the monolith substrate is mainly composed of gamma-phase crystallites with some minor phases (less than 5-10% by weight) of alpha, theta, and delta phases. However, this patent does not teach a monolithic support with an in situ synthesized theta alumina coating for use as a catalyst support.
A need exists for in situ synthesized theta alumina monolithic catalyst supports which can be efficiently manufactured to meet the performance and stability requirements for hydrogenation and hydrotreating applications. The present invention provides such structured materials and methods.